The present invention relates to a method and apparatus for shielding the lens of an optical device, such as a camera or an image projector, from contaminant particles such as rain, dust, and dirt.
There are a variety of optical devices that use lenses. Such devices include devices that receive images, such as video cameras and video monitors, and also include devices that project images, such as video projectors. Some optical devices are used by placing them in remote locations for use without a person attending the optical device, such as a video camera positioned at a strategic vehicle traffic intersection or such as a video projector positioned at the ceiling of a conference room or such as a motion picture projector positioned at a projection room of a movie theater. Other examples of cameras that are located remotely are the so-called xe2x80x9cweb camerasxe2x80x9d or xe2x80x9cwebcamsxe2x80x9d which are accessible through the internet and which permit viewers to visit live scenes at innumerable locations throughout the world.
Contaminant particles such as rain, dust, dirt, insects and insect excreta, etc., may become deposited on the lens of an optical device, and such deposit may occur, for example, by the action of gravity or by air currents such as wind. Such contaminants are undesired since they impair the optical path of the optical device, in other words, the contaminants cause the received or projected image to lose its optical fidelity, and the contaminants may become visible on the image. Accordingly, it is desired that the cleanliness of lenses of optical devices be maintained, that is, it is desired that lenses be kept free contaminants.
In the prior art, optical devices are often placed in and protected by housings such as that illustrated by FIG. 1. FIG. 1 illustrates housing 10 for a traffic camera, or security camera, housed within housing 10 for protection of the camera from the elements of nature such as rain, dust, wind, birds, insects and so forth. Housing 10 is an enclosure which has sides 12 which provide structural support as well as protection and which may be constructed of materials such as metal, plastic, and so forth. Housing has shield 14 which is constructed of transparent glass or plastic and thus is optically transparent. Housing 10 has a mounting bracket 15 which is used to attach housing 10 to a support structure such as to the top of a pole or to eaves under a roof overhang. Data wire 16 provides a communication path for optical data to be transmitted between housing 10 and a remote location. Power line 18 provides an electric power transmission path to housing 10 to provide electric power that is necessary to operate the optical device.
The camera that is housed within housing 10 has lens 20 which is indicated by hidden lines since lens 20 is behind shield 14 and thus lens 20 is protected from the elements and from contaminants by shield 14. Accordingly, housing 10 protects the camera and its lens from contaminants such as dust, dirt, and rain.
In FIG. 1, contaminants 22 are illustrated in a position on shield 14 that would impair the field of view of lens 20. In other words, the field of view of the lens becomes obstructed and the image that is either being received or projected loses its optical fidelity. Contaminants 22 are illustrated as adhering to shield 14 and happen to be positioned in front of lens 20. Contaminants 22 may be undesired water droplets, dirt particles, dust, pollutants, insects, insect excreta, or other contaminants. As used herein, xe2x80x9cfield of viewxe2x80x9d refers to the field of view of lens 20.
Examples of impaired field of views can be observed when one looks at an image of a remotely mounted traffic camera, or a security camera on a windy and rainy day. While a housing 10 with a shield 14 protects the optical device from contaminants 22, the problem then becomes one of maintaining the cleanliness of the shield 14 rather than maintaining the cleanliness of the lens 20. The contaminants 22 will collect on the shield 14 but are nonetheless visible in the field of view since the quality of the image depends upon the cleanliness of shield 14.
Another example of the undesired effect can be observed when contaminants 22 finds their way onto the camera lense in a movie theater. The image of contaminant 22, such as the image of a piece of dust or hair, is projected onto the movie screen to the annoyance of the audience.
The simple solution of the prior art would be to manually clean contaminants 22 from lenses 20 or shields 14 when the deposits become noticeable or to clean the lenses 20 or shields 14 on a scheduled basis.
In the prior art, a solution to this problem is for a maintenance worker to gain access to the protective housing 10 and manually remove the contaminants 22. In other words, the maintenance worker uses a clean tissue or cloth held in the worker""s hand, and perhaps an appropriate cleaning fluid on the tissue or cloth, to wipe the undesired contaminant off shield 14.
There are instances when the protective housing 10 and camera are mounted in a location that is remote, either by being distant and inconvenient to access, or by being relatively inaccessible such as being located at the top of a long pole or otherwise out of convenient reach. Similarly, projectors are often located in relatively inaccessible locations, for example, near the ceiling of a conference room or of a movie theater. In all of these instances, it is inconvenient to manually wipe contaminants 22 from shield 14 due to the relative inaccessibility of the shield 14 to the reach of a workers hand held tissue or cloth. In such instances, it becomes inconvenient and economically costly to maintain the cleanliness of lens shields, such as that illustrated by shield 14.
A prior art is protective housings 10 which have wipers 23 that provide reciprocating motion across shield 14 which is kept stationary with respect to lense 20. However, this prior art has a limitation in that the wiper 23 crosses the field of view of lens 20 which causes loss of optical fidelity, distraction of viewers, and annoyance of viewers, depending upon the viewing or projecting circumstances. This reciprocating motion may be characterized as an obstruction of the field of view of lens 20.
Another prior art is found in the automobile racing field and features shields which are provided with lateral reciprocating motion to cause wiping by wipers that are located outside of the field of view of lens 20. The shields of this prior art are moved back and forth and are moved sufficiently far as to cause contaminants 22 to be wiped by wipers that may be stationary but which are located out of the field of view of lens 20. This prior art may have a limitation in that contaminants 22 may not be completely removed by the wipers and the contaminants may travel back and forth across the field of view. Moreover, the reciprocating motion of the shield of this prior art may cause annoyance to the viewer.
From the limitations in the prior art that are described above, it can be seen that it is desirable to improve the ways for maintaining the cleanliness of the lens shield of optical devices that are protected by a housing.
The present invention is a method and apparatus for shielding the lens and the field of view of an optical device, such as a camera or an image projector, from obstruction by unwanted contaminants such as dust, dirt, rain, and the like. The invention employs a transparent shield positioned to protect the lens from such contaminants. A wiper is positioned to be in contact with the shield but the wiper is also positioned to not obstruct the field of view. A rotation mechanism is used to cause rotation of the shield. Contaminants that may be deposited upon the shield may be wiped from the shield by the wiper yet the wiper does not obstruct the field of view. Rotation of the shield allows a portion of the shield that is obstructed by a contaminant to be rotated away from the field of view. Rotation of the shield allows a portion of the shield that has been wiped to be rotated into the field of view.